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Intercom noise caused by lamps

Discussion in 'Electronic Repair' started by [email protected], Dec 7, 2005.

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  1. Guest

    When the outside lights in this apartment house come on at night by
    photocell control they cause a loud buzzing noise in the buildings'
    intercom system. These lights are the type that come on dim and warm up
    to full brightness over several minutes. There are two large lighting
    units mounted on the front of the building and three smaller units
    mounted in the back. One of the large units is inoperatve in the front
    and one small unit is also not working in the back. Are these what are
    called "high pressure sodium"? Are these known to generate RF
    interference? Is there a ballast in these things, and if so would a
    defective bulb cause the the device to radiate energy into the air
    instead of the load? Can someone please explain how these work and what
    might be the most likely cause of this problem? Thanks for any opinions
    on this. Lenny Stein, Barlen Electronics.
  2. Dave D

    Dave D Guest

    It's impossible to say without a description of the bulbs and the light they
    emit. They could be metal vapour lights like Sodium, Cadmium or Mercury,
    but they could also be HID lamps.

  3. Mark

    Mark Guest

    is it a wireless intercom or wired?


  4. If it's a wireless system I'd say you're out of luck unless you replace
    the lights or get an intercom that can filter out the interference.

    If it's a wired intercom, You may need to make sure the lights and the
    intercom are fed their AC power from different branch circuits.
    Also, you may need to replace the wiring between the intercom panel and
    the individual receivers with shielded wire.

    But first try something simpler - make sure all intercom wire
    connections are clean and tight, and if there are any ground
    connections, make sure they are secure.
  5. James Sweet

    James Sweet Guest

    Are these the crappy Lights of America wall packs with electronic
    ballasts? A friend of mine had several of those and they failed one by
    one, the ballasts were very cheaply made and it wouldn't surprise me if
    they produced a lot of RFI.

    Most HPS uses magnetic ballasts, those shouldn't cause interference,
    except if a lamp is failed the igniter will pulse repeatedly and cause a
    ticking sound to be picked up by nearby audio equipment.
  6. James Sweet

    James Sweet Guest

    Huh? HID is a broad category which covers high pressure sodium, mercury
    vapor and metal halide lamps. There's no such thing as a cadmium vapor
    lamp, at least not outside of specialized lab uses.

    Either way, all HID lamps operate in a similar manner and the ballasts
    are also very similar (though their characteristics must be a proper
    match for the lamp.)
  7. Dave D

    Dave D Guest

    I meant metal halide. Note the time I posted ;-)

  8. Guest

    We found that the problem was caused by a defective lamp. It was either
    arcing (although that wasn't evident) or the fact that there was no
    load to dump the energy into was the problem. In any case a new high
    pressure sodium lamp fixed it. I learned something today...... Lenny
    Stein, Barlen Electronics.
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